Transmission with integrated overload protection for a legged robot

ABSTRACT

An example robot includes: a motor disposed at a joint configured to control motion of a member of the robot; a transmission including an input member coupled to and configured to rotate with the motor, an intermediate member, and an output member, where the intermediate member is fixed such that as the input member rotates, the output member rotates therewith at a different speed; a pad frictionally coupled to a side surface of the output member of the transmission and coupled to the member of the robot; and a spring configured to apply an axial preload on the pad, wherein the axial preload defines a torque limit that, when exceeded by a torque load on the member of the robot, the output member of the transmission slips relative to the pad.

CROSS REFERENCE TO RELATED APPLICATIONS

This U.S. patent application is a continuation of, and claims priorityunder 35 U.S.C. § 120 from, U.S. patent application Ser. No. 15/380,687,filed on Dec. 15, 2016. The disclosure of this prior application isconsidered part of the disclosure of this application and is herebyincorporated by reference in its entirety.

BACKGROUND

An example robot may have a plurality of members forming the robot'slegs and arms. The motion of these members may be controlled byactuators such as hydraulic cylinders and motors. The design of theseactuators determines the performance characteristics of the robot suchas how fast the robot can respond to commands and external disturbances.Design factors that affect performance of the robot may include rotaryinertia of the actuator and gear ratio of a transmission coupledthereto, among other factors.

SUMMARY

The present disclosure describes implementations that relate to atransmission with integrated overload protection for a legged robot. Ina first example implementation, the present disclosure describes arobot. The robot includes: (i) a motor disposed at a joint configured tocontrol motion of a member of the robot; (ii) a transmission includingan input member coupled to and configured to rotate with the motor, anintermediate member, and an output member, where the input member isconfigured to engage the intermediate member and rotate within an openannular space defined by the intermediate member, where the intermediatemember engages the output member, and where the intermediate member isfixed such that as the input member rotates, the output member rotatestherewith at a different speed; (iii) a pad frictionally coupled to aside surface of the output member of the transmission and coupled to themember of the robot; and (iv) a spring configured to apply an axialpreload on the pad, where the axial preload defines a torque limit that,when exceeded by a torque load on the member of the robot, the outputmember of the transmission slips relative to the pad.

In a second example implementation, the present disclosure describes anassembly. The assembly includes: (i) a motor disposed at a jointconfigured to control motion of a member of a robot; (ii) a harmonicdrive comprising a wave generator coupled to and configured to rotatewith the motor, a flexspline, and circular spline, where the flexsplineis fixed such that as the wave generator rotates, the circular splinerotates therewith at a different speed; (iii) a first pad frictionallycoupled to a distal side surface of the circular spline and coupled tothe member of the robot; (iv) a second pad frictionally coupled to aproximal side surface of the circular spline; and (v) a compliant memberconfigured to apply an axial preload on the first and second pads, wherethe axial preload defines a torque limit that, when exceeded by a torqueload on the member of the robot, the circular spline slips relative toat least one of the first or second pads.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects,implementations, and features described above, further aspects,implementations, and features will become apparent by reference to thefigures and the following detailed description.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a configuration of a robotic system, in accordancewith an example implementation.

FIG. 2 illustrates a quadruped robot, in accordance with an exampleimplementation.

FIG. 3 illustrates a biped robot, in accordance with another exampleimplementation.

FIG. 4A illustrates a cross section of a robot leg having a screwactuator, in accordance with an example implementation.

FIG. 4B illustrates a cross section of an upper leg member, inaccordance with an example implementation.

FIG. 5A illustrates a carrier having at least one longitudinal channeldisposed on an outer surface of the carrier, in accordance with anexample implementation.

FIG. 5B illustrates an anti-rotation element, in accordance with anexample implementation.

FIG. 5C illustrates a transparent view of an upper leg member and ananti-rotation element coupled thereto, in accordance with an exampleimplementation.

FIG. 6A illustrates a carrier having rollers coupled thereto, inaccordance with an example implementation.

FIG. 6B illustrates an upper leg member configured to receive a carrierand rails therein, in accordance with an example implementation.

FIG. 6C illustrates a top view cross section of an upper leg member andcomponents disposed therein, in accordance with an exampleimplementation.

FIG. 7 illustrates a configuration with a screw shaft under compression,in accordance with an example implementation.

FIG. 8 illustrates a configuration with a screw shaft under tension, inaccordance with an example implementation.

FIG. 9 illustrates an upper leg member offset relative to a hip joint,in accordance with an example implementation.

FIG. 10 illustrates a motor offset from an upper leg member, inaccordance with an example implementation.

FIG. 11 illustrates a robot leg, in accordance with an exampleimplementation.

FIG. 12A illustrates a diagram showing operation of a harmonic drive, inaccordance with an example implementation.

FIG. 12B illustrates an exploded view of the harmonic drive in FIG. 12A,in accordance with an example implementation.

FIG. 13A illustrates an example drive system with integrated overloadprotection systems, in accordance with an example implementation.

FIG. 13B illustrates a zoomed-in view of the drive system in FIG. 13A,in accordance with an example implementation.

FIG. 13C illustrates an exploded view of the drive system in FIG. 13A,in accordance with an example implementation.

FIG. 14 illustrates an alternative configuration for a drive system of arobot member, in accordance with an example implementation.

FIG. 15A illustrates an integrated motor controller assembly, inaccordance with an example implementation.

FIG. 15B illustrates connecting a torque sensor and an output encoder toa controller, in accordance with an example implementation.

FIG. 15C illustrates thermal management of the assembly shown in FIG.15A, in accordance with an example implementation.

FIG. 15D illustrates a bottom view of a power stage printed circuitboard, in accordance with an example implementation.

FIG. 15E illustrates 12 wires emanating from a stator of a motor, inaccordance with an example implementation.

FIG. 15F illustrates a phase board configured to interface with astator, in accordance with an example implementation.

FIG. 15G illustrates an exploded view of the assembly shown in FIG. 15A,in accordance with an example implementation.

DETAILED DESCRIPTION

The following detailed description describes various features andoperations of the disclosed systems with reference to the accompanyingfigures. The illustrative implementations described herein are not meantto be limiting. Certain aspects of the disclosed systems can be arrangedand combined in a wide variety of different configurations, all of whichare contemplated herein.

Further, unless context suggests otherwise, the features illustrated ineach of the figures may be used in combination with one another. Thus,the figures should be generally viewed as component aspects of one ormore overall implementations, with the understanding that not allillustrated features are necessary for each implementation.

Additionally, any enumeration of elements, blocks, or steps in thisspecification or the claims is for purposes of clarity. Thus, suchenumeration should not be interpreted to require or imply that theseelements, blocks, or steps adhere to a particular arrangement or arecarried out in a particular order.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to skill in theart, may occur in amounts that do not preclude the effect thecharacteristic was intended to provide.

I. Example Robotic Systems

FIG. 1 illustrates an example configuration of a robotic system that maybe used in connection with the implementations described herein. Therobotic system 100 may be configured to operate autonomously,semi-autonomously, and/or using directions provided by user(s). Therobotic system 100 may be implemented in various forms, such as a bipedrobot, quadruped robot, or some other arrangement. Furthermore, therobotic system 100 may also be referred to as a robot, robotic device,or mobile robot, among other designations, and could be part of anexoskeleton or human assisting device.

As shown in FIG. 1, the robotic system 100 may include processor(s) 102,data storage 104, and controller(s) 108, which together may be part of acontrol system 118. The robotic system 100 may also include sensor(s)112, power source(s) 114, mechanical components 110, and electricalcomponents 116. Nonetheless, the robotic system 100 is shown forillustrative purposes, and may include more or fewer components. Thevarious components of robotic system 100 may be connected in any manner,including wired or wireless connections. Further, in some examples,components of the robotic system 100 may be distributed among multiplephysical entities rather than a single physical entity. Other exampleillustrations of robotic system 100 may exist as well.

Processor(s) 102 may operate as one or more general-purpose hardwareprocessors or special purpose hardware processors (e.g., digital signalprocessors, application specific integrated circuits, etc.). Theprocessor(s) 102 may be configured to execute computer-readable programinstructions 106, and manipulate data 107, both of which are stored inthe data storage 104. The processor(s) 102 may also directly orindirectly interact with other components of the robotic system 100,such as sensor(s) 112, power source(s) 114, mechanical components 110,and/or electrical components 116.

The data storage 104 may be one or more types of hardware memory. Forexample, the data storage 104 may include or take the form of one ormore computer-readable storage media that can be read or accessed byprocessor(s) 102. The one or more computer-readable storage media caninclude volatile and/or non-volatile storage components, such asoptical, magnetic, organic, or another type of memory or storage, whichcan be integrated in whole or in part with processor(s) 102. In someimplementations, the data storage 104 can be a single physical device.In other implementations, the data storage 104 can be implemented usingtwo or more physical devices, which may communicate with one another viawired or wireless communication. As noted previously, the data storage104 may include the computer-readable program instructions 106 and thedata 107. The data 107 may be any type of data, such as configurationdata, sensor data, and/or diagnostic data, among other possibilities.

The controller 108 may include one or more electrical circuits, units ofdigital logic, computer chips, and/or microprocessors that areconfigured to (perhaps among other tasks), interface between anycombination of the mechanical components 110, the sensor(s) 112, thepower source(s) 114, the electrical components 116, the control system118, and/or a user of the robotic system 100. In some implementations,the controller 108 may be a purpose-built embedded device for performingspecific operations with one or more subsystems of the robotic system100.

The control system 118 may monitor and physically change the operatingconditions of the robotic system 100. In doing so, the control system118 may serve as a link between portions of the robotic system 100, suchas between mechanical components 110 and/or electrical components 116.In some instances, the control system 118 may serve as an interfacebetween the robotic system 100 and another computing device. Further,the control system 118 may serve as an interface between the roboticsystem 100 and a user. The instance, the control system 118 may includevarious components for communicating with the robotic system 100,including a joystick, buttons, and/or ports, etc. The example interfacesand communications noted above may be implemented via a wired orwireless connection, or both. The control system 118 may perform otheroperations for the robotic system 100 as well.

During operation, the control system 118 may communicate with othersystems of the robotic system 100 via wired or wireless connections, andmay further be configured to communicate with one or more users of therobot. As one possible illustration, the control system 118 may receivean input (e.g., from a user or from another robot) indicating aninstruction to perform a particular gait in a particular direction, andat a particular speed. A gait is a pattern of movement of the limbs ofan animal, robot, or other mechanical structure.

Based on this input, the control system 118 may perform operations tocause the robotic system 100 to move according to the requested gait. Asanother illustration, a control system may receive an input indicatingan instruction to move to a particular geographical location. Inresponse, the control system 118 (perhaps with the assistance of othercomponents or systems) may determine a direction, speed, and/or gaitbased on the environment through which the robotic system 100 is movingen route to the geographical location.

Operations of the control system 118 may be carried out by theprocessor(s) 102. Alternatively, these operations may be carried out bythe controller 108, or a combination of the processor(s) 102 and thecontroller 108. In some implementations, the control system 118 maypartially or wholly reside on a device other than the robotic system100, and therefore may at least in part control the robotic system 100remotely.

Mechanical components 110 represent hardware of the robotic system 100that may enable the robotic system 100 to perform physical operations.As a few examples, the robotic system 100 may include physical memberssuch as leg(s), arm(s), and/or wheel(s). The physical members or otherparts of robotic system 100 may further include actuators arranged tomove the physical members in relation to one another. The robotic system100 may also include one or more structured bodies for housing thecontrol system 118 and/or other components, and may further includeother types of mechanical components. The particular mechanicalcomponents 110 used in a given robot may vary based on the design of therobot, and may also be based on the operations and/or tasks the robotmay be configured to perform.

In some examples, the mechanical components 110 may include one or moreremovable components. The robotic system 100 may be configured to addand/or remove such removable components, which may involve assistancefrom a user and/or another robot. For example, the robotic system 100may be configured with removable arms, hands, feet, and/or legs, so thatthese appendages can be replaced or changed as needed or desired. Insome implementations, the robotic system 100 may include one or moreremovable and/or replaceable battery units or sensors. Other types ofremovable components may be included within some implementations.

The robotic system 100 may include sensor(s) 112 arranged to senseaspects of the robotic system 100. The sensor(s) 112 may include one ormore force sensors, torque sensors, velocity sensors, accelerationsensors, position sensors, proximity sensors, motion sensors, locationsensors, load sensors, temperature sensors, touch sensors, depthsensors, ultrasonic range sensors, infrared sensors, object sensors,and/or cameras, among other possibilities. Within some examples, therobotic system 100 may be configured to receive sensor data from sensorsthat are physically separated from the robot (e.g., sensors that arepositioned on other robots or located within the environment in whichthe robot is operating).

The sensor(s) 112 may provide sensor data to the processor(s) 102(perhaps by way of data 107) to allow for interaction of the roboticsystem 100 with its environment, as well as monitoring of the operationof the robotic system 100. The sensor data may be used in evaluation ofvarious factors for activation, movement, and deactivation of mechanicalcomponents 110 and electrical components 116 by control system 118. Forexample, the sensor(s) 112 may capture data corresponding to the terrainof the environment or location of nearby objects, which may assist withenvironment recognition and navigation. In an example configuration,sensor(s) 112 may include RADAR (e.g., for long-range object detection,distance determination, and/or speed determination), LIDAR (e.g., forshort-range object detection, distance determination, and/or speeddetermination), SONAR (e.g., for underwater object detection, distancedetermination, and/or speed determination), VICON® (e.g., for motioncapture), one or more cameras (e.g., stereoscopic cameras for 3Dvision), a global positioning system (GPS) transceiver, and/or othersensors for capturing information of the environment in which therobotic system 100 is operating. The sensor(s) 112 may monitor theenvironment in real time, and detect obstacles, elements of the terrain,weather conditions, temperature, and/or other aspects of theenvironment.

Further, the robotic system 100 may include sensor(s) 112 configured toreceive information indicative of the state of the robotic system 100,including sensor(s) 112 that may monitor the state of the variouscomponents of the robotic system 100. The sensor(s) 112 may measureactivity of systems of the robotic system 100 and receive informationbased on the operation of the various features of the robotic system100, such the operation of extendable legs, arms, or other mechanicaland/or electrical features of the robotic system 100. The data providedby the sensor(s) 112 may enable the control system 118 to determineerrors in operation as well as monitor overall operation of componentsof the robotic system 100.

As an example, the robotic system 100 may use force sensors to measureload on various components of the robotic system 100. In someimplementations, the robotic system 100 may include one or more forcesensors on an arm or a leg to measure the load on the actuators thatmove one or more members of the arm or leg. As another example, therobotic system 100 may use one or more position sensors to sense theposition of the actuators of the robotic system. For instance, suchposition sensors may sense states of extension, retraction, or rotationof the actuators on arms or legs.

As another example, the sensor(s) 112 may include one or more velocityand/or acceleration sensors. For instance, the sensor(s) 112 may includean inertial measurement unit (IMU). The IMU may sense velocity andacceleration in the world frame, with respect to the gravity vector. Thevelocity and acceleration sensed by the IMU may then be translated tothat of the robotic system 100 based on the location of the IMU in therobotic system 100 and the kinematics of the robotic system 100.

The robotic system 100 may include other types of sensors not explicateddiscussed herein. Additionally or alternatively, the robotic system mayuse particular sensors for purposes not enumerated herein.

The robotic system 100 may also include one or more power source(s) 114configured to supply power to various components of the robotic system100. Among other possible power systems, the robotic system 100 mayinclude a hydraulic system, electrical system, batteries, and/or othertypes of power systems. As an example illustration, the robotic system100 may include one or more batteries configured to provide charge tocomponents of the robotic system 100. Some of the mechanical components110 and/or electrical components 116 may each connect to a differentpower source, may be powered by the same power source, or be powered bymultiple power sources.

Any type of power source may be used to power the robotic system 100,such as electrical power or a gasoline engine. Additionally oralternatively, the robotic system 100 may include a hydraulic systemconfigured to provide power to the mechanical components 110 using fluidpower. The power source(s) 114 may charge using various types ofcharging, such as wired connections to an outside power source, wirelesscharging, combustion, or other examples.

The electrical components 116 may include various mechanisms capable ofprocessing, transferring, and/or providing electrical charge or electricsignals. Among possible examples, the electrical components 116 mayinclude electrical wires, circuitry, and/or wireless communicationtransmitters and receivers to enable operations of the robotic system100. The electrical components 116 may interwork with the mechanicalcomponents 110 to enable the robotic system 100 to perform variousoperations. The electrical components 116 may be configured to providepower from the power source(s) 114 to the various mechanical components110, for example. Further, the robotic system 100 may include electricmotors. Other examples of electrical components 116 may exist as well.

Although not shown in FIG. 1, the robotic system 100 may include a body,which may connect to or house appendages and components of the roboticsystem. As such, the structure of the body may vary within examples andmay further depend on particular operations that a given robot may havebeen designed to perform. For example, a robot developed to carry heavyloads may have a wide body that enables placement of the load.Similarly, a robot designed to reach high speeds may have a narrow,small body that does not have substantial weight. Further, the bodyand/or the other components may be developed using various types ofmaterials, such as metals or plastics. Within other examples, a robotmay have a body with a different structure or made of various types ofmaterials.

The body and/or the other components may include or carry the sensor(s)112. These sensors may be positioned in various locations on the roboticsystem 100, such as on the body and/or on one or more of the appendages,among other examples.

On its body, the robotic system 100 may carry a load, such as a type ofcargo that is to be transported. The load may also represent externalbatteries or other types of power sources (e.g., solar panels) that therobotic system 100 may utilize. Carrying the load represents one exampleuse for which the robotic system 100 may be configured, but the roboticsystem 100 may be configured to perform other operations as well.

As noted above, the robotic system 100 may include various types oflegs, arms, wheels, and so on. In general, the robotic system 100 may beconfigured with zero or more legs. An implementation of the roboticsystem with zero legs may include wheels, treads, or some other form oflocomotion. An implementation of the robotic system with two legs may bereferred to as a biped, and an implementation with four legs may bereferred as a quadruped. Implementations with six or eight legs are alsopossible. For purposes of illustration, biped and quadrupedimplementations of the robotic system 100 are described below.

FIG. 2 illustrates a quadruped robot 200, according to an exampleimplementation. Among other possible features, the robot 200 may beconfigured to perform some of the operations described herein. The robot200 includes a control system, and legs 204A, 204B, 204C, 204D connectedto a body 208. Each leg may include a respective foot 206A, 206B, 206C,206D that may contact a surface (e.g., a ground surface). Further, therobot 200 is illustrated with sensor(s) 210, and may be capable ofcarrying a load on the body 208. Within other examples, the robot 200may include more or fewer components, and thus may include componentsnot shown in FIG. 2.

The robot 200 may be a physical representation of the robotic system 100shown in FIG. 1, or may be based on other configurations. Thus, therobot 200 may include one or more of mechanical components 110,sensor(s) 112, power source(s) 114, electrical components 116, and/orcontrol system 118, among other possible components or systems.

The configuration, position, and/or structure of the legs 204A-204D mayvary in example implementations. The legs 204A-204D enable the robot 200to move relative to its environment, and may be configured to operate inmultiple degrees of freedom to enable different techniques of travel. Inparticular, the legs 204A-204D may enable the robot 200 to travel atvarious speeds according to the mechanics set forth within differentgaits. The robot 200 may use one or more gaits to travel within anenvironment, which may involve selecting a gait based on speed, terrain,the need to maneuver, and/or energy efficiency.

Further, different types of robots may use different gaits due tovariations in design. Although some gaits may have specific names (e.g.,walk, trot, run, bound, gallop, etc.), the distinctions between gaitsmay overlap. The gaits may be classified based on footfall patterns—thelocations on a surface for the placement the feet 206A-206D. Similarly,gaits may also be classified based on ambulatory mechanics.

The body 208 of the robot 200 connects to the legs 204A-204D and mayhouse various components of the robot 200. For example, the body 208 mayinclude or carry sensor(s) 210. These sensors may be any of the sensorsdiscussed in the context of sensor(s) 112, such as a camera, LIDAR, oran infrared sensor. Further, the locations of sensor(s) 210 are notlimited to those illustrated in FIG. 2. Thus, sensor(s) 210 may bepositioned in various locations on the robot 200, such as on the body208 and/or on one or more of the legs 204A-204D, among other examples.

FIG. 3 illustrates a biped robot 300 according to another exampleimplementation. Similar to robot 200, the robot 300 may correspond tothe robotic system 100 shown in FIG. 1, and may be configured to performsome of the implementations described herein. Thus, like the robot 200,the robot 300 may include one or more of mechanical components 110,sensor(s) 112, power source(s) 114, electrical components 116, and/orcontrol system 118.

For example, the robot 300 may include legs 304 and 306 connected to abody 308. Each leg may consist of one or more members connected byjoints and configured to operate with various degrees of freedom withrespect to one another. Each leg may also include a respective foot 310and 312, which may contact a surface (e.g., the ground surface). Likethe robot 200, the legs 304 and 306 may enable the robot 300 to travelat various speeds according to the mechanics set forth within gaits. Therobot 300, however, may utilize different gaits from that of the robot200, due at least in part to the differences between biped and quadrupedcapabilities.

The robot 300 may also include arms 318 and 320. These arms mayfacilitate object manipulation, load carrying, and/or balancing for therobot 300. Like legs 304 and 306, each arm may consist of one or moremembers connected by joints and configured to operate with variousdegrees of freedom with respect to one another. Each arm may alsoinclude a respective hand 322 and 324. The robot 300 may use hands 322and 324 (or end-effectors) for gripping, turning, pulling, and/orpushing objects. The hands 322 and 324 may include various types ofappendages or attachments, such as fingers, grippers, welding tools,cutting tools, and so on.

The robot 300 may also include sensor(s) 314, corresponding to sensor(s)112, and configured to provide sensor data to its control system. Insome cases, the locations of these sensors may be chosen in order tosuggest an anthropomorphic structure of the robot 300. Thus, asillustrated in FIG. 3, the robot 300 may contain vision sensors (e.g.,cameras, infrared sensors, object sensors, range sensors, etc.) withinits head 316.

II. Example Electromechanical Actuators For a Robot

In examples, hydraulic actuators could be used to actuate members of arobot. A hydraulic system may include a pump and accumulator at acentral location on the robot and configured to provide pressurizedhydraulic fluid through pipes and/or hoses to hydraulic actuatorscoupled to the members of the robot. In this configuration, theactuation inertia of the pump and accumulator is decoupled from inertiaprovided to the ground surface as the robot moves. Due to the decouplingof inertias, hydraulic robotic systems are characterized by highbandwidth for position and force control responsiveness. However,hydraulic systems have disadvantages such as potential hydraulic fluidleaks, complexity of plumbing, and unsuitability of existing hydraulicpower units to smaller robots.

Electromechanical actuators alleviate at least some disadvantages ofhydraulic actuators because there are no leaks or complex plumbinginvolved with operating electromechanical actuators. Further,electromechanical systems may be more efficient than hydraulic systems.However, electromechanical actuators may have disadvantages compared tohydraulic systems. For instance, while the rotating inertia of a robotmember driven by a hydraulic actuator might have a linear relationshipwith a diameter of the actuator for a given strength, the rotatinginertia of a robot member driven by an electromechanical actuator may beproportional to the square of the diameter of the actuator's rotatingassembly and is influenced by the gear ratio of the transmission for thegiven strength. Further, reflected inertia of a hydraulic actuator mightbe negligible compared to the inertial of a member (e.g., leg) of arobot, whereas reflected inertial of an electromechanical may depend oninertias of the motor and the transmission multiplied by the square ofthe gear ratio of the transmission. Thus, for large robots,electromechanical actuators may have a high inertia that limitsresponsiveness and performance characteristics of the robot.

For robots smaller in size, electromechanical actuators could bedesigned, as described in this disclosure, to achieve high performancecharacteristics compared to corresponding hydraulic actuators. Disclosedherein are systems, actuators, configurations, and apparatuses thatreduce rotating inertia of robot members to allow for achieving highpeak torques capable of providing sufficiently high accelerationssuitable for high performance robots.

a. Example Screw Actuator for a Joint of a Robot

In examples, a knee joint of a robot may experience high accelerationsthat results, for example, from actuating the robot to move fast (e.g.,run or jog). High accelerations could also result when the robot issubjected to a disturbance at its leg, and the robot responds withmoving the leg, and particularly the knee joint, at a high accelerationto maintain balance. In some examples, an electric motor could becoupled to the knee joint of robot, such that rotational motion of themotor causes a lower leg member of the robot to rotate relative to anupper leg member that is coupled to the lower leg member at the kneejoint. In this configuration, the rotational inertia of the motor maylimit the responsiveness of the robot, and may thus reduce effectivenessof force control strategies of the lower leg member.

Further, if a transmission is coupled to the motor, and thattransmission has a particular gear ratio that allows for speed reductionand torque amplification, the rotational inertia at the knee joint isproportional to the square of the gear ratio. So, a higher gear ratiothat allows for higher torques may lead to a higher rotational inertia,thus reducing the responsiveness of the robot.

Reducing the rotational inertia at the knee joint may improveresponsiveness of the robot. In an example, a screw actuator could beused to drive the knee joint of the robot, because screw actuators arelight and slender and thus have low inertia compared to other actuatorconfigurations. Further, using a screw actuator allows for a reduceddistal mass at the knee, which may in turn allow for higher accelerationcapabilities.

FIG. 4A illustrates a cross section of a robot leg having a screwactuator 400, in accordance with an example implementation. An electricmotor 402 is located at or near a hip joint 403 of the robot. In otherexamples, the electric motor 402 may be located at an upper leg portionof the robot. Whether the electric motor 402 is located at an upper legportion or the hip joint 403, the mass of the motor 402 is shifted awayfrom a knee joint 404. Thus, these configurations may reduce the distalmass at the knee joint 404 of the robot, and therefore the rotationalinertia at the hip joint 403 is reduced.

The screw actuator 400 is a mechanical linear actuator that translatesrotational motion to linear motion with little friction. In an example,the screw actuator 400 may be a planetary roller screw type and mayinclude a screw shaft 406 and a nut 408. The screw shaft 406 may have amulti-start V-shaped thread on a periphery thereof. The V-shaped threadprovides a helical raceway for multiple rollers radially arrayed aroundthe screw shaft 406 and encapsulated by the nut 408. The rollers are notshown in FIG. 4A to reduce visual clutter in the drawings.

The nut 408 is threaded on an interior peripheral surface thereof tointerface with the V-shaped thread of the screw shaft 406. The pitch ofthe thread of the screw shaft 406 may be the same as the pitch of theinternal thread of the nut 408. The rollers spin in contact with, andserve as low-friction transmission elements between, the screw shaft 406and the nut 408. The rollers may have a single-start thread with convexflanks that limit friction at the rollers' contacts with the screw shaft406 and the nut 408. The rollers may orbit the screw shaft 406 as theyspin (in the manner of planet gears to a sun gear), and could thus bereferred to as planetary, or satellite, rollers.

The motor 402 is coupled to the screw shaft 406, and thus as the motor402 rotates, the screw shaft 406 rotates therewith. Rotation of thescrew shaft 406 results in axial or longitudinal travel of the nut 408.

The motor 402 and the screw actuator 400 are housed within a body (e.g.,a machined aluminum body) of an upper leg member 410 of the robot. Theupper leg member 410 is coupled to a lower leg member 412 at the kneejoint 404.

The nut 408 is housed within a proximal end 413 of a carrier 414 andinterfaces with the carrier 414 at a shoulder 416 such that as the nut408 travels along the screw shaft 406, the carrier 414 also moveslinearly within the upper leg member 410. Herein, the term “proximalend” refers to the end of the carrier 414 closer to the motor 402.

The nut 408 is axially constrained within the proximal end 413 of thecarrier 414 by the shoulder 416 and a nut 417 that captures the nut 408axially in the carrier 414. Further, the nut 408 may be rotationallyconstrained to the carrier 414 to preclude rotation of the nut 408relative to the carrier 414. For instance, the nut 408 may be coupled tothe carrier 414 via a key-keyway configuration.

A linkage mechanism is coupled to the carrier 414 to facilitateconverting the linear motion of the carrier 414 into a rotation motionof the lower leg member 412 relative to the upper leg member 410 aboutthe knee joint 404. As an example, the linkage mechanism may include afirst link 418 (e.g., a connecting rod) that is coupled to a distal end420 of the carrier 414. Herein, the term “distal end” refers to the endof the carrier 414 that is farthest from the motor 402. In anotherexample, the first link 418 may be trunnion-mounted to the carrier 414at other locations that are closer to the motor 402.

The first link 418 may be coupled to a second link 422 at a joint 424,and the second link may be coupled at the knee joint 404 at knee pivot426. The lower leg member 412 is also coupled to the knee joint 404 atthe knee pivot 426. In this configuration, the linear motion of thecarrier 414 causes the first link 418 to move, thereby causing thesecond link 422 and the lower leg member 412 to rotate about the kneepivot 426. Other linkage configurations could be used. For instance, afour bar mechanism could be used to achieve different transmission curveshapes.

The direction of rotation of the motor 402 determines the direction ofrotation of the lower leg member 412 relative to the upper leg member410. For instance, if the motor 402 rotates in a given direction (e.g.,clockwise), the nut 408 and the carrier 414 may extend and push thefirst link 418. As a result, the second link 422 rotates in a clockwisedirection from a perspective of a viewer of FIG. 4A about the knee pivot426. As a result, the lower leg member 412 may also rotate clockwisefrom a perspective of a viewer of FIG. 4A, thus for example pushing afoot 428 against a surface 430.

Conversely, if the motor 402 rotates in the opposite direction (e.g.,counter-clockwise), the nut 408 and the carrier 414 may retract and pullthe first link 418. As a result, the second link 422 rotates in acounter-clockwise direction from a perspective of a viewer of FIG. 4Aabout the knee pivot 426, thereby causing the lower leg member 412 tocurl upward. Thus, alternating between rotating the motor 402 clockwiseand counter-clockwise causes the robot to take steps (e.g., walk or runat a particular pace).

In an example, the motor 402 may include an encoder 431. The encoder 431is configured to generate a signal indicative of a rotary position of arotor of the motor 402. The encoder 431 may provide informationindicative of the rotary position of the rotor to a controller of therobot. The controller may implement a closed-loop feedback control onthe rotary position of the motor 402 so as to accurately position thenut 408 within the upper leg member 410.

By placing the motor 402 closer to the hip joint 403 and using the screwactuator 400, the distal mass at the knee joint 404 is reduced. Further,using the screw actuator 400 as a speed reducer instead of a rotarygearbox may reduce the effective rotational inertia because the screwactuator 400 has a reduced rotational inertia compared to a rotarygearbox.

FIG. 4B illustrates a cross section of the upper leg member 410, inaccordance with an example implementation. As shown in FIG. 4B, theupper leg member 410 may house a bearing carrier 432. The bearingcarrier 432 may be seated along a conical seat 434 that protrudes inwardfrom an internal surface of the upper leg member 410.

The bearing carrier 432 houses a bearing 435 configured to allow thescrew shaft 406 to rotate freely. An outer diameter of an outer race ofthe bearing 435 interfaces with an interior peripheral surface of thebearing carrier 432. The outer race of the bearing 435 is retainedagainst a shoulder 436 formed of a stepped surface on the interiorperipheral surface of the bearing carrier 432.

Further, the screw shaft 406 includes a shoulder 438 formed of a steppedsurface on an exterior peripheral surface of the screw shaft 406. Theshoulder 438 interfaces with an inner race of the bearing 435. This way,the bearing 435 is axially constrained between the shoulder 438 and theshoulder 436.

As shown in FIG. 4B, the first link 418 is coupled to the distal end 420of the carrier 414 via a pin 440. The first link 418 forms an angle □relative to a longitudinal axis 442 of the screw shaft 406. Thus, as thescrew shaft 406 rotates causing the nut 408 and the carrier 414 to pushthe first link 418, the first link 418 may impart a reaction force ontocarrier 414, which is transferred to the nut 408 and the screw shaft406. The reaction force can be resolved into a longitudinal axial forcecomponent 444 acting along the longitudinal axis 442 and a radial oroff-axis force component 446 acting perpendicular to the longitudinalaxis 442 and the interior surface of the upper leg member 410.

To reduce effects of the off-axis force component 446 and the frictionthat results thereof, a slider bearing 448 is mounted between anexternal peripheral surface of the carrier 414 at the distal end 420 andthe interior peripheral surface of the upper leg member 410. The sliderbearing 448 may be configured to reduce friction and facilitate axialmotion of the carrier 414 within the upper leg member 410. Particularly,the slider bearing 448 may be configured to react the off-axis forcecomponent 446 on the nut 408 to the upper leg member 410 and constrainthe forces resulting from interaction between the first link 418 and thecarrier 414 along the axis 442. In an example, the slider bearing 448may be made of Teflon®.

In an example, another slider bearing 450 could be mounted between anexternal peripheral surface of the carrier 414 at the proximal end 413and the interior peripheral surface of the upper leg member 410. Inthese examples, the slider bearings 448 and 450 may operate as guidebushings that allow the carrier 414 to be subjected to the axial forcecomponent 444 while reacting the off-axis force component 446 andreducing friction.

As mentioned above, the axial force component 444 acting on the carrier414 is transferred to the nut 408 and the screw shaft 406. The screwshaft 406 interfaces with the bearing 435 at the shoulder 438, and thusthe bearing 432 is subjected to the axial force component 444. The axialforce component 444 is then transferred from the bearing 435 via theshoulder 436 to the bearing carrier 432.

An axial load cell 440 may be disposed on the exterior peripheralsurface of the bearing carrier 432. Thus, the axial load cell 440 isalso subjected to the axial force component 444, which is imparted tothe carrier 414 and the screw shaft 406 during operation of the robotleg. The axial load cell 440 may generate an electric signal that isproportional to the axial force component 444 imparted to the screwshaft 406. The electric signal may be provided to a controller of therobot or the leg members of the robot.

In an example, the controller may use the encoder 431 and the axial loadcell 440 to implement various control strategies based on condition ofthe robot, the environment of the robot, and the commanded acceleration.For example, in a first control strategy, the controller may implement aclosed-loop position control on the rotary position of the motor 402 asmentioned above. In a second control strategy, the controller mayimplement closed-loop force control for the force exerted by the foot428 on the surface 430. This control strategy may allow for highacceleration capabilities for the robot leg. In a third controlstrategy, the controller may implement closed-loop position and forcecontrol where the force control loop may be used to dampen motion of therobot leg. These control strategies are examples for illustration, andother control strategies could be implemented.

In examples, the carrier 414, and the components coupled thereto such asthe nut 408, may be precluded from rotation about the longitudinal axis442 via anti-rotation mechanisms or configurations. FIGS. 5A-5Cillustrate an anti-rotation configuration for the carrier 414, inaccordance with an example implementation. Specifically, FIG. 5Aillustrates the carrier 414 having at least one longitudinal channel 500disposed on an outer surface of the carrier 414, in accordance with anexample implementation. As shown in FIG. 5A, the longitudinal channel500 is disposed between the proximal end 413 and the distal end 420 ofthe carrier 414. In examples, the longitudinal channel 500 may take theform of a slot that is machined longitudinally on the outer surface ofthe carrier 414.

FIG. 5B illustrates an anti-rotation element 502, in accordance with anexample implementation. The anti-rotation element 502 includes a curvedplate 504 and a nub 506 that protrudes from a concave surface of thecurved plate 504. The anti-rotation element 502 is configured to becoupled to an outer surface of the upper leg member 410 such that thenub 506 protrudes radially inward within the upper leg member 410 andengages the longitudinal channel 500.

As an example, the curved plate 504 may have holes such as hole 508. Theouter surface of the upper leg member 410 may have corresponding holes.Fasteners could be used to couple the curved plate 504 to the upper legmember 410 via the holes in the curved plate 504 and the correspondingholes in the upper leg member 410. Further, the upper leg member 410 mayhave a central hole that corresponds to and is configured to receive thenub 506 therethrough.

FIG. 5C illustrates a transparent view of the upper leg member 410 andthe anti-rotation element 502 coupled thereto, in accordance with anexample implementation. The outer surface of the upper leg member 410,or a portion thereof, may be curved to match the curvature of theconcave surface of the curved plate 504. This way, the concave surfaceof the curved plate 504 may conform to a profile or contour of the outersurface of the upper leg member 410 when coupled thereto.

The nub 506 protrudes through the outer surface of the upper leg member410 and engages with the longitudinal channel 500 of the carrier 414.With this configuration, as the carrier 414 moves axially within theupper leg member 410, the nub 506 precludes the carrier 414 fromrotating about the longitudinal axis 442. In examples, the nub 506 maybe made of a material (e.g., Teflon) that reduces friction with thelongitudinal channel 500 as the carrier 410 moves within the upper legmember 410.

Other example anti-rotation mechanisms could be implemented. FIGS. 6A-6Cillustrate another anti-rotation mechanism, in accordance with anexample implementation. Specifically, FIG. 6A illustrates a carrier 600having roller(s) 602 coupled thereto, in accordance with an exampleimplementation. FIG. 6A shows one roller 602 on one side of the carrier600. Another roller may be coupled to the carrier 600 on the other sidethereof. In examples, more rollers similar to the roller 602 may becoupled to the carrier 600. The roller 602 is configured to roll withina rail 604, and the roller corresponding to the roller 602 on the otherside of the carrier 600 is configured to roll within a rail 606 that isparallel to the rail 604. Both rollers are collectively referred to asroller(s) 602.

The rails 604 and 606 are configured to constrain the roller(s) 602therein. In this manner, the rails 604 and 606 may operate as tracks forthe roller(s) 602 such that the rails 604 and 606 and the roller(s) 602form a roller element bearing configuration. This configuration reducesfriction as the carrier 600 moves within the robot leg. Additionally, inan example, a slider bearing 607 made, for example, of Teflon®, could bedisposed about an outer surface of the carrier 600 to interface with aninterior surface of the robot leg to further reduce friction.

Both rails 604 and 606 have holes such as holes 608A, 608B, 608C, 608D,and 608E formed therein that may be configured to receive fasteners tofixedly mount the rails 604 and 606 to the robot leg as described belowwith respect to FIG. 6B. Because the rails 604 and 606 are fixedlymounted to the robot leg and at the same time they constrain motion ofthe roller(s) 602 therein, the carrier 600 is precluded from rotationabout a longitudinal axis 609 thereof.

FIG. 6B illustrates an upper leg member 610 configured to receive thecarrier 600 and the rails 604 and 606 therein, in accordance with anexample implementation. The upper leg member 610 may be similar to theupper leg member 410, but may additionally have a pattern of holes 612on an outside surface thereof. The pattern of holes 612 corresponds tothe holes disposed in the rails 604 and 606. For instance, holes 614A,614B, 614C, and 614D of the pattern of holes 612 may correspond to theholes 608A, 608B, 608C, and 608D of the rail 604, respectively.Fasteners could be then used to fixedly mount the rails 604 and 606within the upper leg member 610.

FIG. 6C illustrates a top view cross section of the upper leg member 610and components disposed therein, in accordance with an exampleimplementation. As shown in FIG. 6C, a roller carriage 616 is coupled toa distal end of the carrier 600 and is disposed perpendicular to thelongitudinal axis 609. The roller(s) 602 are coupled to the rollercarriage 616 and configured to roll within the rails 604 and 606, whilebeing constrained therein. Particularly, at least one roller 602 iscoupled to first end of the roller carriage 616 and rollers within therail 604 and another roller 602 is coupled to a second end of the rollercarriage 616 opposite the first end and configured to roll within therail 606. While FIGS. 6A and 6C illustrate the rails 604 and 606 asseparate components from the upper leg member 610, in some examples, therails 604 and 606 could alternatively be integrated with or built-in theinner surface of the upper leg member 610.

An axial load cell 618 is disposed closer to the motor 402 compared tothe axial load cell 440 described above. The axial load cell 618 mayalso be of a different type. For instance, while the axial load cell 440is depicted as a column-style load cell, the axial load cell 618 is abending beam style load cell. Other styles and locations for load cellscould be used as well.

As the robot moves and the lower leg member 412 shown in FIG. 4A rotatesrelative to the upper leg member 410 or 610, the screw shaft 406 issubjected to alternating compressive and tensile forces. For instance,if the screw shaft 406 is rotating in a direction (e.g.,counter-clockwise) that causes the nut 406 to retract, thus pulling thecarrier 414 and the first link 418, the screw shaft 406 is undertension. Whereas, if the screw shaft 406 is rotating in an oppositedirection (e.g., clockwise) that causes the nut 406 to extend, thuspushing the carrier 414 and the first link 418, the screw shaft 406 isunder compression.

Further, for the robot to move, the lower leg member 412, which may bein contact with a ground surface (e.g., the surface 430), pushes againstthe ground surface. Even when the robot is standing in place, the lowerleg member 412 exerts a pushing force against the ground surface tomaintain the robot standing and balanced. Whether the robot is moving orstanding, the pushing force against the ground surface may cause eithera tensile or compressive force in the screw shaft 406 based on ageometric configuration of the first link 418 relative to the knee pivot426.

FIG. 7 illustrates a configuration with the screw shaft 406 undercompression, in accordance with an example implementation. Theconfiguration shown in FIG. 7 is similar to the configuration of FIG.4A. In this configuration, the first link 418 is coupled to the lowerleg member 412 at the joint 424, which is located between the knee pivot426 and the foot 428. As a result, when the lower leg member 412 pushesagainst the surface 430, a compressive force is applied along a lengthof the first link 418 in a direction of arrow 700. This compressiveforce is transmitted to the carrier 414 and through the nut 408 to thescrew shaft 406. Thus, in this configuration, the screw shaft 406 isunder compression.

FIG. 8 illustrates a configuration with the screw shaft 406 undertension, in accordance with an example implementation. In thisconfiguration, the first link 418 is coupled to the lower leg member 412at a joint 800 such that a knee pivot 802 is disposed between the joint800 and the foot 428. As a result, when the lower leg member 412 pushesagainst the surface 430, a tensile force is applied along a length ofthe first link 418 in a direction of arrow 804. This tensile force istransmitted to the carrier 414 through the nut 408 to the screw shaft406. Thus, in this configuration, the screw shaft 406 is under tension.

Either of the configurations of FIG. 7 or 8 could be used. However, insome examples, the robot may be subjected to environmental conditionsthat could cause forces in the screw shaft 406 that might besufficiently high to cause buckling therein. In these examples, theconfiguration of FIG. 8 could be used so as to preclude buckling in thescrew shaft 406. The peak extension force of leg of the robot istypically higher than the peak retraction force and the configuration ofFIG. 8 puts the screw shaft 406 in tension during high extension forceevents.

Other configurations for the robot leg could be implemented. FIG. 9illustrates the upper leg member 410 offset relative to the hip joint403, in accordance with an example implementation. As shown, theassembly including the upper leg member 410, and the components therein,is offset relative to the hip joint 403. This configuration mayalleviate packaging constraints imposed by limiting a length of theupper leg member 410 based on the location of the hip joint 403. Inother words, the length of the upper leg member 410 could be increasedin the configuration of FIG. 9 relative to the configuration of FIG. 4A,for example. Alternatively, in other examples, offsetting the upper legmember 410 relative to the hip joint 403 may facilitate reducing anoverall length from the knee pivot 426 to the hip joint 403.

Further, in the configurations discussed above, the motor 402 isdisposed inline with the screw shaft 406. In some examples, theseconfigurations could cause the upper leg member 410 or 610 to berelatively long. Other configurations could be used to shorten the upperleg member 410 or 610.

FIG. 10 illustrates the motor 402 offset from the upper leg member 410,in accordance with an example implementation. As shown, by removing themotor 402 from the upper leg member 410 and offsetting it relative tothe upper leg member 410, the upper leg member 410 could be shortened.In this configuration a belt drive could be disposed as a speedreduction pre-stage between the motor 402 and the screw shaft 406. Thisspeed reduction pre-stage could allow for reducing a speed reductionratio of the screw actuator 400. Reducing the speed reduction ratio ofthe screw actuator 400 may reduce the rotational inertia, leading tohigher performance characteristics as described below.

Generally, a roller screw may provide more bearing points or area than aball screw within a given volume, and may thus lower contact stresses.Also, a roller screw can be more compact for a given load capacity whileproviding similar efficiency (e.g., 75%-90%) as ball screws at low tomoderate speeds, and maintain relatively high efficiency at high speeds.A roller screw may further achieve better positioning accuracy, loadrating, rigidity, speed, acceleration, and lifetime compared to a ballscrew. However, a ball screw could be cheaper than a roller screw, andthus it may be desirable to use a ball screw for some applications.

b. Example Transmission with Integrated Clutch for Overload Protection

Rotational inertia affects the position and force control responsivenessof a robot. The effective rotational inertia at a joint of the robot maydepend on the rotational inertia of the motor coupled to the joint andthe rotational inertia of a transmission coupled to the motor. Thetransmission may have a particular gear ratio that allows for speedreduction and torque amplification, and the effective rotational inertiaat the joint is proportional to the square of the gear ratio. So, ahigher gear ratio that allows for higher torques may lead to a higherrotational inertia, thus reducing the responsiveness of the robot.

Typically, a large motor and low gear ratio may provide lower outputinertia compared to a small motor and high gear ratio, but at theexpense of greater mass. Thus, using a large motor to achieve highertorques and strengths may lead to a high rotational inertia, whichreduces the responsiveness of the robot. Even if a small motor is used,a transmission with a high gear reduction ratio may also lead to a higheffective rotational inertia.

In selecting a motor for a joint of a robot, one approach may entaildetermining a maximum torque that the joint is expected to be subjectedto and select a motor that can achieve that maximum torque. However,this approach may lead to high effective rotational inertias. Forexample, in impact situations, such as when a leg of a robot hits aground surface unexpectedly or the leg is subjected to a sudden impactby an object, the impact may cause the motor to spin at high speeds torespond to the impact and maintain the robot's balance. Particularly,the impact causes the motor and input side of the transmission toaccelerate rapidly. The resulting inertial torque gets amplified by thegear ratio causing high torque at the joint, which may damage thetransmission and/or the leg structure. The reflected inertia in thissituation may be determined based on the sum of the rotational inertiaof the motor and the transmission multiplied by the square of thereduction ratio of the transmission. Selecting a motor that can achievea maximum torque that occurs in such impact situations may lead to alarge motor with a corresponding large rotational inertia.

Another approach may entail impedance matching. Specifically, the motorand the transmission at a joint are selected to have a reflected oroutput inertia that is equal to the inertia of the robot member that iscontrolled by the joint. This approach may increase the accelerationcapability of the joint.

In another example, the motor may be used to directly drive the memberwithout a transmission coupled thereto. This way, the reflected inertiamay be reduced. However, without a transmission, there is no torqueamplification and the maximum torque is limited by the torque that themotor could achieve. Even if a transmission with a reduced gear ratio isused, the motor may then have a larger size to compensate for thereduced torque amplification at the transmission, thus leading toexcessive weight and size.

An improved approach presented herein may entail integrating an overloadprotection system within the motor or the transmission. The overloadprotection system may isolate the transmission from high torquesencountered in impact situations. This way, a reduced size transmissionthat can achieve appropriate torques and accelerations may be selected.A smaller transmission may have lower inertia, thus allowing for asmaller motor to achieve desired acceleration, because the overallinertial is reduced.

Disclosed herein are systems and apparatuses that involve integrating aclutch to a harmonic drive transmission to allow for reducing a size ofthe motor and transmission, thus reducing mass and inertia to improveresponsiveness of the robot. The integrated clutch system describedbelow, may, for example, be used at a hip joint of the robot or otherjoints.

FIG. 11 illustrates a robot leg, in accordance with an exampleimplementation. As mentioned above, a screw actuator such as the screwactuator 400 may be used instead of a rotary gearbox to drive the kneejoint 404. The screw actuator 400 may allow for reducing the distal massat the knee joint 404. The distal mass affects the inertial of the leg,and placing mass closer to the hip reduces the inertial torque requiredat the hip joints. The screw actuator 400 may also reduce the effectiverotational inertia because the screw actuator 400 has a reducedrotational inertia compared to a rotary gearbox.

Additionally, a motor and transmission with an overload protectionsystem described herein may be coupled to the hip joint 403 to reducethe rotational inertia thereat. For instance, the motor and transmissionmay be installed along one or both of an x-axis 1100 and y-axis 1102 atthe hip joint 403.

FIG. 12A illustrates a diagram showing operation of a harmonic drive1200, and FIG. 12B illustrates an exploded view of the harmonic drive1200, in accordance with an example implementation. The harmonic drive1200 is used herein as an example transmission system to operate as aspeed reducer and torque amplifier. Harmonic drives are characterized byzero-backlash characteristics, a wide range of reduction ratios, weightand space savings compared to other transmission systems, highpositional accuracy, and repeatability. However, other transmissionsystems, such as a cycloidal transmission, could be used.

As shown in FIG. 12A, the harmonic drive 1200 includes three maincomponents: an input member that may be referred to as a wave generator1202; an intermediate member that may be referred to as a flexspline1204; and an outer member that may be referred to as a circular spline1206. As illustrated in FIG. 12B, the wave generator 1202 may include athin raced ball bearing 1208 that is fitted onto an elliptical hub 1210.The elliptical hub 1210 might not appear elliptical in FIG. 12B becausethe dimensional difference between the major and minor axes thereof issmall. The wave generator 1202 operates as a torque converter and isconnected to an input shaft from a motor, and thus operates as the inputto the harmonic drive 1200.

The flexspline 1204 is a thin cylindrical cup made, for example, fromalloy steel with external teeth 1212 on exterior peripheral surface ofan open end of the cup. The flexspline 1204 is radially compliant orflexible, but is torsionally stiff. When the wave generator 1202 isinserted into the flexspline 1204, the wave generator 1202 interfaceswith the external teeth 1212 of the flexspline 1204 at the open endthereof. Thus, the open end of the flexspline 1204 takes on theelliptical shape of the wave generator 1202.

The circular spline 1206 is a rigid ring with internal teeth 1214. Whenthe harmonic drive 1200 is assembled, the internal teeth 1214 of thecircular spline 1206 engage with the external teeth 1212 of theflexspline 1204 across a major axis 1216 of the elliptically shaped wavegenerator 1202. The circular spline 1206 may have more teeth than theflexspline 1204. For instance, the circular spline 1206 may have twomore teeth than the flexspline 1204.

In examples, the flexspline 1204 is used as the output and may thus beconnected to an output flange, whereas the circular spline 1206 isfixedly mounted. In other examples, the circular spline 1206 is used asthe output and may thus be connected to an output flange, whereas theflexspline 1204 is fixedly mounted. In the example description providedbelow, the circular spline 1206 is allowed to rotate and may beconnected to an output, whereas the flexspline 1204 is fixedly mounted.However, other configurations could be used.

When the elliptical hub 1210 of the wave generator 1202 is rotated, theflexspline 1204 deforms to the shape of elliptical hub 1210 and does notslip over the outer peripheral surface of the ball bearing 1208. As aresult, the external teeth 1212 of the flexspline 1202 engage theinternal teeth 1214 of the circular spline 1206 at two opposite regionsacross the major axis 1216 of the wave generator 1202. For every 180degree rotation of the wave generator 1202, the internal teeth 1214 ofthe circular spline 1206 are advanced by one tooth in relation to theexternal teeth 1212 of the flexspline 1204. Thus, each complete rotationof the wave generator 1202 may result in the circular spline 1206 movingby two teeth from its original position relative to the flexspline 1204.

With a harmonic drive such as the harmonic drive 1200, a wide range ofgear reduction ratios are possible in a small volume (e.g., a ratio from30:1 up to 320:1). As mentioned above, having a low ratio may reducereflected or output inertia of the transmission, i.e., the harmonicdrive 1200, to facilitate high performance capabilities of the robot. Toprotect the harmonic drive 1200 in high impact situations, an overloadprotection system is integrated therein as described below.

FIG. 13A illustrates an example drive system with integrated overloadprotection systems, FIG. 13B illustrates a zoomed-in view of the drivesystem in FIG. 13A, and FIG. 13C illustrates an exploded view of thedrive system in FIG. 13A, in accordance with an example implementation.FIGS. 13A-13E are described together. The drive system in FIGS. 13A-13Ccould be coupled to either or both axes 1100 and 1102 of the hip joint403, or any other joint of the robot. The description below refers to amotor and transmission at the hip joint 403 to drive a robot leg.However, the systems described herein could be used at any other jointto drive any other member (e.g., arms) of the robot.

A motor 1300 is mounted within a housing 1302 at the hip joint 403 ofthe robot. The housing 1302 is coupled to the robot via a flange 1306and fasteners such as fasteners 1308A and 1308B.

A rotor of the motor 1300 is coupled to a shaft 1310 configured torotate with the rotor. A wave generator 1312 that could be similar tothe wave generator 1202 is coupled to and configured to rotate with theshaft 1310. The wave generator 1312 interfaces with a toothed portion ofa flexspline 1314 that could be similar to the flexspline 1204. Theflexspline 1314 is fixedly mounted via fasteners such as fasteners 1315Aand 1315B to a load cell or torque sensor 1316, which in turn is fixedlymounted to the housing 1302. External teeth of the teethed portion ofthe flexspline 1314 engage with internal teeth of a circular spline 1318that could be similar to the circular spline 1206. Teeth of theflexspline 1314 and the circular spline 1318 are not shown in FIGS.13A-13C to reduce visual clutter in the drawings.

With this configuration, as the wave generator 1312 rotates with theshaft 1310, the circular spline 1318 rotates about a longitudinal axis1319 because the flexspline 1314 is fixed. A proximal side surface ofthe circular spline 1318 interfaces with a first clutch pad 1320, and adistal side surface of the circular spline 1318 interfaces with a secondclutch pad 1322. Herein, proximal side refers to the side closer to themotor 1300, and distal side refers to the side that is farther from themotor 1300.

The clutch pads 1320 and 1322 have friction material mounted to theirsurfaces that interface with respective surfaces of the circular spline1318. Thus, as long as the clutch pads 1320 and 1322 are sufficientlypreloaded against or biased toward the respective surfaces of thecircular spline 1318, the clutch pads 1320 and 1322 rotate with thecircular spline 1318.

The clutch pad 1320 also interfaces with and is coupled to a presserplate 1324. Similarly, the clutch pad 1322 also interfaces with and iscoupled to an output flexure 1326. In an example, the clutch pad 1320may be glued via any kind of adhesive to the presser plate 1324, and theclutch pad 1322 may be glued via any kind of adhesive to the outputflexure 1326. Other fastening means could be used to couple the clutchpad 1320 to the presser plate 1324 and the clutch pad 1322 to the outputflexure 1326. In an example, the presser plate 1324 could be made ofaluminum. However, other materials are possible as well. Also, inanother example, the clutch pads 1320 and 1322 may be glued to thecircular spline 1318 and allowed to slide relative to the presser plate1324 and the output flexure 1326. In still another example, the clutchpads 1320 and 1322 might not be glued to any other component and may beallowed to slide along any of the four surfaces, two surfaces for eachclutch pad.

A Belleville spring 1328 is disposed between a robot member 1330 (e.g.,a leg member) and the output flexure 1326. The Belleville spring 1328exerts an axial biasing force on the output flexure 1326 so as to applyan axial preload on the clutch pad 1322. The axial preload on the clutchpad 1322 similarly preloads the clutch pad 1320 because the axialpreload is transferred through the circular spline 1318 to the clutchpad 1320, which is constrained by the presser plate 1324.

The axial preload may keep the clutch pads 1320 and 1322 frictionallycoupled to the circular spline 1318 until a predetermined torque limitis exceeded. If the torque limit is exceeded, the static friction limitof the clutch pads 1320 and 1322 may be exceeded, and the circularspline 1318 might slip relative to the clutch pads 1320 and 1322.Therefore, the torque limit may be referred to as the slip torque.

The torque limit is based on the spring rate of the Belleville spring1328. Shims such as shim 1332 could be added between the Bellevillespring 1328 and the robot member 1330 to vary the axial preload on theclutch pads 1320 and 1322 and thus vary the torque limit.

The output flexure 1326 may be torsionally stiff but axially flexible.For instance, the output flexure can be made of a flexible material suchas titanium. In an example, the output flexure 1326 may be made of asofter material compared to the Belleville spring 1328. For instance,the output flexure 1326 may have a spring rate that is less than (e.g.,10%) of the spring rate of the Belleville spring 1328. In this example,the Belleville spring 1328 provides the dominant axial preload forcecompared to the force applied by the output flexure 1326 on the clutchpad 1322. However, other configurations are possible. The output flexure1326 is configured to torsionally connect the robot member 1330 to theclutch pad 1322 while allowing axial motion thereof to accommodate wearand to also allow the Belleville spring 1328 to preload the clutch pad1322 against the circular spline 1318.

In an example, a constraint ring 1334 may be disposed between thepresser plate 1324 and the robot member 1330. The constraint ring 1334has an open annular space in which the circular spline 1318 and theclutch pads 1320 and 1322 are disposed and constrained. In an example,the constraint ring 1334 may be made of aluminum; however, othermaterials are possible as well.

A radial array of fasteners or bolts, such as bolts 1335A and 1335B, maybe configured to hold the assembly including the presser plate 1324, theconstraint ring 1334, the output flexure 1326, and the robot member 1330together. Due to the axial preload applied by the Belleville spring1328, the clutch pads 1320 and 1322 and the circular spline 1318 aresqueezed between the output flexure 1326 and the presser plate 1324. Assuch, the clutch pads 1320 and 1322 and the circular spline 1318 arealso part of the assembly held together by the radial array of boltsincluding the bolts 1335A and 1335B

As mentioned above, as the wave generator 1312 rotates, the circularspline 1318 rotates because the flexspline 1314 is fixed. The circularspline 1318 rotates at a reduced rotational speed relative to the wavegenerator 1312 but can apply an amplified torque relative to the torqueapplied by the wave generator 1312. As the circular spline 1318 rotates,the clutch pads 1320 and 1322 frictionally coupled thereto also rotate,and the torque transferred from the circular spline 1318 to the clutchpads 1320 and 1322 is transferred to the robot member 1330 via twopaths. The first path includes transferring the torque from the circularspline 1318 through the clutch pad 1322 to the output flexure 1326,which is coupled to the robot member 1330 via the array of bolts. Thesecond path includes transferring the torque from the circular spline1318 through the clutch pad 1320 to the presser plate 1324, which iscoupled to the robot member 1330 via the array of bolts.

A cross roller bearing 1336 may be mounted to an external peripheralsurface of the constraint ring 1334 between the constraint ring 1334 andan interior surface of the housing 1302. The cross roller bearing 1336facilitates rotation of the robot member 1330 relative to the housing1302 and may be configured to handle radial, thrust, and moment reactionloads applied to the robot member 1330.

The system described above facilitates overload protection of the motor1302 and the harmonic drive while allowing for reducing speed reductionratio of the harmonic drive, and thus reducing the rotational inertiathereof. As an example, the motor 1302 could be rotating fast to try tomove the robot member 1330 to a particular location. As the robot member1330 moves, it might hit or bump into an unexpected or undetectedobject. As a result, without an overload protection system, the motor1302 may be forced to stop in a small period of time (e.g., 1millisecond). A torque that may amount to four times the torque capacityof the harmonic drive may be applied thereto to stop it. If the harmonicdrive is designed to be able to withstand or apply such a high torque,the harmonic drive would be larger and exhibit a larger rotationalinertia.

As another example, the robot may impact an object, e.g., the robot mayfall on a ground surface from a particular height, and the impact maycause a high torque to be applied to the harmonic drive that could causedamage. In another example, the robot may be in an inactive state (e.g.,power to the robot via a battery for example is shut down, a cable isbroken, or a controller malfunction occurred). If an object impacts therobot in such a state, the controller of the robot might not have powerand might thus not send signals to electrically operated safetycomponents to protect the robot. In all these examples, the harmonicdrive and the motor 1302 may be subjected to a high torque that couldcause damage to their components.

With the overload protection systems described in FIGS. 13A-13C, thecircular spline 1318 would slip relative to the clutch pads 1320 and1322 if the load torque on the robot member 1330 exceeds the torquelimit specified by the axial preload of the Belleville spring 1332. Inthis manner, the harmonic drive (i.e., the circular spline 1318) isdecoupled for a period of time from the robot member 1330 and is thusprotected from the high load torque. Further, as the circular spline1318 slips relative to the clutch pads 1320 and 1322, kinetic energy ofthe robot member 1330 is dissipated due to the friction between thecircular spline 1318 and the clutch pads 1320 and 1322. Once the loadtorque falls back below the torque limit, the harmonic drive reengageswith the robot member 1330.

An advantage of the overload protection system is that the clutch pads1320 and 1320 are integrated within the harmonic drive and interfacewith the components thereof (i.e., the circular spline 1318). Thisintegration allows for a compact design as opposed to adding a clutchsystem inline with the harmonic drive, which would require morelongitudinal space.

Another advantage is that the output flexure 1326 is configured to allowthe robot member 1330 to reverse its direction of motion with zerobacklash. Most robot members such as the robot member 1330 operate intwo directions. For instance, if the robot member 1330 is a leg of therobot, the motor 1302 may spin in one direction to swing the leg in acorresponding direction, then stop the leg and spin in a reversedirection to swing the leg in an opposite direction. Accurate control ofposition, speed, and acceleration of the leg in addition to control ofthe force applied by the leg may depend on several factors includingzero backlash when reversing the direction of motion.

If there is backlash, then one clutch pad of the two clutch pads 1320and 1322 may be engaged with the circular spline 1318 upon reversingdirection while the other clutch pad might not be engaged. Thus, theengaged clutch pad may start to slip relative to the circular spline1318 and then after a period of time, the other clutch pad may start tobe loaded, and then both clutch pads 1320 and 1322 would slip togetherrelative to the circular spline 1318.

Because of the flexibility of the output flexure 1326 and Bellevillespring 1328, they can accommodate axial movement of components of thedrive system relative to each other. For example, they can accommodatewear in the clutch pads 1320 and 1322, axial movement of the robotmember 1330 relative to the harmonic drive, etc. without overstressingthe components. Thus, the output flexure 1326 and the Belleville spring1328 can compensate for manufacturing tolerance of the variouscomponents.

At the same time, the output flexure 1326 pushes against the clutch pad1322 and causes the clutch pads 1320 and 1322 to remain in contact withthe circular spline 1318, thus eliminating backlash. Therefore, even ifthe motor 1302 and the circular spline 1318 stop and then theirdirection of rotation is reversed, the output flexure 1326 may ensuresmooth movement of the robot member 1330.

Further, the output flexure 1326 may cause the torque load to be equallyshared between the two clutch pads 1320 and 1322. The force applied bythe output flexure 1326 maintains contact between the clutch pad 1322against the circular spline 1318. The same force applied by the outputflexure 1326 further squeezes the clutch pad 1322 against the circularspline 1318 along with the clutch pad 1320 against the presser plate1324. This way, the clutch pads 1320 and 1322 are equally loaded as thecircular spline 1318 rotates.

In some examples, grease or other lubricants could be applied tocomponents of the harmonic drive or bearings in the drive systemillustrated in FIGS. 12A-13B. Lubricants reduce wear of, and frictionbetween, the meshing components of the drive system. In these examples,seals such as O-rings 1338A and 1338B could be used to keep grease awayfrom the clutch pads 1320 and 1322. Particularly, the O-ring 1338A couldkeep the grease away from the clutching interface between the clutch pad1320 and the proximal face of the circular spline 1318. And, the O-ring1338B could keep the grease away from the clutching interface betweenthe clutch pad 1322 and the distal face of the circular spline 1318.This way, the grease might not affect the torque limit (i.e., the sliptorque) determined at least partially by the spring rate of theBelleville spring 1328.

However, in other example implementations, the O-rings 1338A and 1338Bmight not be used. The axial preload imposed by the Belleville spring1328 may then be adjusted, e.g., by choosing a Belleville spring with adifferent spring rate, to accommodate the presence of grease. Changingthe spring rate of the Belleville spring may tune performance of theclutch pads 1320 and 1322 to operate at a reduced coefficient offriction resulting from the presence of grease.

As mentioned above, as the wave generator 1312 rotates with the shaft1310 of the motor 1302, the circular spline 1318 also rotates due to theflexspline 1314 being fixed. As the circular spline 1318 rotates, theassembly including the clutch pads 1320-1322, the presser plate 1324,and the constraint ring 1334 also rotates. The robot member 1330 alsorotates via the radial array of bolts (e.g., the bolts 1335A-1335B). Aslong as the load torque applied to the robot member 1330 does not exceedthe torque limit, the assembly and the robot member 1330 rotate with thecircular spline 1318. If the load torque exceeds the torque limit, thecircular spline 1318 slips relative to the clutch pads 1320 and 1320.

In a torque overload situation, the oval shape of the wave generator1312 may distort the circular spline 1318 into an oval shape as well.When the torque falls back below the torque limit, the clutch pad 1320and 1322 reengage the circular spline 1318, and may thus cause its shapeto remain ovalized. Such a distorted oval shape of the circular spline1318 may result in torque pulsations at the robot member 1330.

To preclude keeping the circular spline 1318 in a distorted shape state,a constraint bushing 1340 may be inserted between an external peripheralsurface of the circular spline 1318 and an internal peripheral surfaceof the constraint ring 1334. The clearance between the externalperipheral surface of the circular spline 1318 and the internalperipheral surface of the constraint ring 1334, and thus the thicknessof the constraint bushing 1340, is small. For instance, the interferencecould be 1/1000th of an inch.

In examples, the constraint bushing 1340 may be made of a plasticmaterial, e.g., Polyether ether ketone (PEEK) material or otherpolymeric material. Plasticity of the constraint bushing 1340 imparts arelatively low stiffness thereto, thus facilitating insertion of theconstraint busing 1340 with a light press fit in the interference. Thisconfiguration accommodates production variations in dimensions andconcentricity of the circular spline 1318 and the constraint ring 1334.

During operation of the robot, respective temperatures of the constraintbushing 1340, the circular spline 1318, and the constraint ring 1334 mayrise. The circular spline 1318 and the constraint ring 1334 may expandand contract at different rates because they could be made of differentmaterial having different coefficients of thermal expansion. However,the plastic material of the constraint bushing 1340 may become softer,and thus accommodate any dimensional variations in the circular spline1318 and the constraint ring 1334 due to temperature changes.

Further, the constraint bushing 1340 couples the circular spline 1318and the constraint ring 1334 such that they move as one assembly. Thus,when a shape of the circular spline 1318 changes (e.g., ovalized) undertorque load, the circular spline 1318 and the constraint ring 1334 maybe distorted together along with the constraint bushing 1340. This way,when the torque load falls back below the torque limit, the circularspline 1318, the constraint bushing 1340, and the constraint ring 1334may spring back together to an undistorted shape. Also, the circularspline 1318, the constraint bushing 1340, and the constraint ring 1334may deform less because of the presence of the constraint bushing 1340as opposed to having a gap or clearance. Thus, the presence of theconstraint bushing 1340 may prevent torque pulsations.

The circular spline 1318 and the constraint ring 1334 could be made ofdifferent materials. For instance, the circular spline 1318 could bemade of cast iron, while the constraint ring 1334 may be made oftitanium. Allowing the circular spline 1318 to be in contact with theconstraint ring 1334 might cause binding and galling therebetween. Theconstraint bushing 1340 operates as an interface between the circularspline 1318 and the constraint ring 1334 to preclude such binding andgalling, while preventing torque pulsations as described above.

The components and configurations described above with respect to FIGS.12A-13C are example components and configurations and are not meant tobe limiting. Other components and configurations could be used. Forexample, instead of using two clutch pads, one clutch pad may be used.In another example, a clutch pad may be used on one side of the circularspline 1318, and any type of friction material including bare metal onmetal contact could be used on the other side thereof.

In the configuration described above, the overload protective clutchingoperation takes place on the interface between the clutch pads 1320 and1322 and the circular spline 1318. In another example implementation,the clutching operation could take place on the interface between theclutch pad 1320 and the output flexure 1326 and between the clutch pad1322 and the presser plate 1324. In this example, the clutch pads 1320and 1320 may be integrated with the circular spline 1318. In otherwords, the proximal and distal faces of the circular spline could havefriction material disposed thereon. Further, in other examples, othercomponents may be added between the circular spline 1318 and the clutchpads 1320 and 1322. In another example variation, the output flexure1404 and the Belleville spring 1328 may be integrated into one flexiblecomponent. Also, a Belleville spring is used herein as an example, andin other implementations any other type of springs or flexible,compliant elements could be used.

FIG. 14 illustrates an alternative configuration for a drive system of arobot member 1400, in accordance with an example implementation. Asshown in FIG. 14, a bolt ring 1402 replaces the presser plate 1324 andthe constraint ring 1334. In other words, the presser plate 1324 and theconstraint ring 1334 can be integrated into a single component shown asthe bolt ring 1402 in FIG. 14.

An output flexure 1404, which may perform similar operations as theoutput flexure 1326, is coupled to the robot member 1400 at a centralregion 1406 via a bolt array including bolts such as bolt 1408. Incontrast to the bolts 1335A-1335B, bolts such as bolt 1410 in FIG. 14couple the bolt ring 1402 to the robot member 1400 without coupling theoutput flexure 1402 thereto.

These variations are examples for illustration only, and those skilledin the art will appreciate that other arrangements and other elements(e.g., components, interfaces, orders, and groupings of components,etc.) can be used instead, and some elements may be omitted altogetheraccording to the desired results.

c. Example Motor-Controller Integration Configuration

An example robot may include several joints to control motion ofcorresponding members of the robot. As an example, a quadruped robot mayhave 17 joints that connect and control the members of the robot (e.g.,arms, legs, etc.). In examples, many of these joints may have respectivemotors configured to move the members of the robot. Each of the motorsis controlled by a controller that receives several inputs (e.g., fromsensors) and accordingly provide control signals to the motor to controlthe joint and members of the robot.

In an example, a controller may be placed at a central location on therobot and wires could be connected between the controller and thevarious motors and sensors. This configuration may involve complexwiring and long wires that may reduce the reliability of the robot andincrease the probability of failure.

In other examples, each joint may have a respective motor and acontroller for that motor. Integrating and co-locating the motor and itscontroller may improve the reliability of the robot. Such integrationmay reduce the complexity of the wiring configuration.

Disclosed herein are systems and apparatuses having integrated motor andcontroller assemblies to reduce complexity of the robot and increasereliability. Particularly, a motor and its controller may be integratedinto a compact package proximate to each other to facilitate sharingsensors and thermal management components. With the configurationsdisclosed herein, the number and lengths of wires are reduced, thusenhancing the reliability of the robot by reducing points of potentialfailure. These configurations may thus reduce the likelihood of failureand downtime for the robot and lower the maintenance cost of the robot.

FIG. 15A illustrates an integrated motor controller assembly 1500, inaccordance with an example implementation. As shown, the assembly 1500includes a motor 1502 disposed within a housing 1504. The housing 1504includes heatsink fins 1506 that are circumferentially spaced apart in acircular array about an exterior surface of the housing 1504.

The assembly 1500 includes a controller 1508 that may include one ormore printed circuit board (PCBs). For example, the controller 1508 mayinclude a power stage PCB 1510 and a logic stage PCB 1512. The powerstage PCB 1510 may for example include the power electronics that mightinclude solid-state electronics configured for the control andconversion of electric power provided to the windings of a stator of themotor 1502. For instance, the power stage PCB 1510 may include aplurality of field-effect transistors (FETs).

The logic stage PCB 1512 may, for example, include one or moremicroprocessors and data storage including instructions to be executedby the one or more microprocessors to perform various control operationsfor the motor 1502. The power stage PCB 1510 and logic stage PCB 1512are in communication with each other. In the example implementationshown in FIG. 15A, the power stage PCB 1510 and logic stage PCB 1512 arejuxtaposed or arranged on respective axially spaced planes. In otherexamples, however, they may be disposed in a different configuration andin some examples components of the power stage PCB 1510 and componentsof the logic stage PCB 1512 may be integrated into a single PCB.

The rotor of the motor 1502 is coupled to a shaft 1514 that transmitsthe rotary motion of the rotor to a transmission such as a harmonicdrive 1516. In an example, the shaft 1514 may be hollow and a magnet1518 may be disposed at a proximal end therein. Herein, the term“proximal end” refers to the end of the shaft 1514 that is closer to thecontroller 1508, whereas a “distal end” of the shaft 1514 refers to theend that is coupled to the harmonic drive 1516.

As shown, the shaft 1514 extends through the power stage PCB 1510 suchthat the magnet 1518 is disposed closer to and facing the logic stagePCB 1512. Further, the logic stage PCB 1512 may include a rotaryposition sensor 1520 (e.g., a magnetoresistive or Hall Effect sensor)disposed thereon facing the magnet 1518.

The magnet 1518 may be diametrically magnetized such that as the shaft1514 and the magnet 1518 coupled thereto rotate, the sensor 1520provides information indicative of the rotary position of the shaft 1514to the controller 1508. This information is used by the controller 1508to control commutation of the motor 1502. With this configuration, therotary position sensor 1520 of the motor 1502 is integrated into themotor controller 1508. This configuration contrasts with otherconfigurations where a rotary position sensor of a motor is disposedcloser to the motor and wires connect the sensor with the controller,thus increasing the likelihood of wire breakage and failure.

The assembly 1500 may further include another rotary position sensor oroutput encoder 1522 configured to provide information indicative of therotary position of a robot member 1524 to the logic stage PCB 1512. Forinstance, the output encoder 1522 may be coupled to a presser plate1526, which may be coupled to the robot member 1524. By measuring therotary position of the presser plate 1526, the output encoder 1522provides measurements of the rotary position of the robot member 1524.

In this manner, the controller 1508 receives information indicating therotary positions of the motor 1502 and the robot member 1524. As such,the controller 1508 may determine whether a circular spline 1528 of theharmonic drive 1516 slipped due to overloading as described above withrespect to FIGS. 13A-14. The assembly 1500 further includes a torqueload cell or torque sensor 1530 configured to measure the torque load onthe harmonic drive 1516.

FIG. 15B illustrates connecting the torque sensor 1530 and the outputencoder 1522 to the controller 1508, in accordance with an exampleimplementation. Wires from the torque sensor 1530 and the output encoder1522 may be routed to and combined at a connection 1532 fixed to thetorque sensor 1530, which is fixed to housing of the stator of the motor1502. The wires may then be connected to a flexible PCB 1534 that mightbe configured to perform preliminary processing on the signals from thetorque sensor 1530 and the output encoder 1522 (e.g., signalamplification, filtering, etc.).

Wires from the flexible PCB 1534 may then be routed through the housing1504 to one or more connectors 1536. The connectors 1536 may beconfigured to mate with corresponding connectors 1537 (shown in FIGS.15D and 15G) coupled to the controller 1508 (e.g., to the power stagePCB 1510) through a sealing grommet 1538. With this configuration,having the output encoder 1522 and the torque sensor 1530 close to thecontroller 1508 facilitates integration and shortening the wires, thusimproving reliability of the robot.

The configuration shown in FIGS. 15A-15B may also allow for sharingthermal management components between the motor 1502 and the controller1508. FIG. 15C illustrates thermal management of the assembly 1500, andFIG. 15D illustrates a bottom view of the power stage PCB 1510, inaccordance with an example implementation.

FETs 1540 may be disposed on a surface of the power stage PCB 1510 thatfaces away from the logic stage PCB 1512. Also, a thermal sensor 1542 isdisposed on the same surface of the power stage PCB 1510 having the FETs1540 disposed thereon. A thermal interfacial material 1544 separates thepower stage PCB 1510 and the components mounted thereon (e.g., the FETs1540 and the thermal sensor 1542) from ribs 1546 that protrude radiallyinward from an interior peripheral surface of the housing 1504. In otherexample implementations, any other thermal coupling surfaces orthermally conductive structures could be used instead of or in additionto the ribs 1546. For instance, instead of distinct ribs, a solidsurface could be used. Other examples are possible.

The thermal interfacial material 1544 could be a flexible, compliantmaterial that can compensate for height variations of components mountedon the power stage PCB 1510. The thermal interfacial material 1544includes thermally conductive materials, which may increase thermalcontact conductance across jointed solid surfaces in order to increasethermal transfer efficiency. Rather than leaving the gaps between thepower stage PCB 1510 and the ribs 1546 filled with air, which is a poorthermal conductor, the thermal interfacial material 1544 provides for anenhanced thermal efficiency and transfer. Particularly, thermal transferbetween the power stage PCB 1510 and the ribs 1546 is enhanced.

The thermal interfacial material 1544 may include a silicon basedmaterial or a non-silicon based material and may take several forms. Forinstance, the thermal interfacial material 1544 may include a paste orthermal grease made, for example, of silicone oil filled with aluminumoxide, zinc oxide, or boron nitride. The thermal interfacial material1544 may also use micronized or pulverized silver. In examples, thethermal interfacial material 1544 may include fiberglass forreinforcement.

The ribs 1546 are configured to also provide a heat path for the heatgenerated by the motor 1502, and particularly by its stator windings.With this configuration, the controller 1508 and the motor 1502 share acommon thermal management and dissipation arrangement. The arrows inFIG. 15D illustrate example heat paths for both the motor 1502 and thecontroller 1508. Heat generated from the motor 1502 and the controller1508 is conducted through the ribs 1546 to the fins 1506 disposed on thehousing 1504.

A shroud 1548 encloses a fan 1550 that, when activated, draws air anddirects the air toward the fins 1506. In this manner, the fan 1550 mayenhance heat dissipation at the fins 1506 and cool both the motor 1502and the controller 1508.

The thermal sensor 1542 is placed on the power stage PCB 1510 on thesame surface having the FETs 1540 as mentioned above, and thus providesinformation indicative of the temperature of the FETs 1540 and othercomponents of the controller 1508. The thermal sensor 1542 may also bein contact with or proximate to the ribs 1546. The thermal sensor 1542may thus also provide information indicative of the temperature of thestator of the motor 1502, which is adjacent to the ribs 1546. With thisconfiguration, both the motor 1502 and the controller 1508 share acommon thermal sensor. The sensor information provided by the thermalsensor 1542 to the controller 1508 may be used to control when tooperate the fan 1550 and at what speed.

The thermal sensor 1542 may also be used for safety monitoring of themotor 1502 and the harmonic drive 1516 (shown in FIG. 15A). Forinstance, the thermal sensor 1542 may indicate that the temperature ofthe stator exceeds a threshold temperature, which may in turn indicatethat the motor 1502 or the harmonic drive 1516 is overloaded.Alternatively, the high temperature may indicate that components of theharmonic drive 1516 might be misaligned and that maintenance may be due.

In this manner, the thermal sensor 1542 may indicate to the controller1508 the state of the various components of the controller 1508 itselfand the motor 1502. The controller 1508 may then determine whether tocontinue operation of the joint or shut it down for safety reasons.Thus, integrating the motor 1502 and the controller 1508 as shown inFIGS. 15A-15D allows for having a common thermal sensor for both ofthem, thereby reducing the lengths and extent of wiring associated withthermal management.

If the motor 1502 and the controller 1508 each has its own thermalsensor, then double the number of sensors and wiring would be added tothe robot. For a quadruped robot that has 17 joints, the amount andextent of wiring increases significantly, thus reducing reliability ofthe robot as a whole. Integration leads to reduction in component countand wiring complexity, which may have enhance overall reliability of therobot.

In examples, as shown in FIG. 15C, logic stage stand-offs such asstand-off 1551A could be used to provide for a consistent distancebetween the logic stage PCB 1512 and the power stage PCB 1510. Thesestand-offs may ensure that components of both PCBs do not touch eachother.

Further, power stage stand-offs such as stand-off 1551B could be used toprovide for a consistent gap or distance between the FETs 1540 and theribs 1546. The FETs 1540 could be “live” and thus may have a highvoltage that could damage other components if conducted thereto. Thepower stage stand-offs preclude the FETs 1540 from contacting any othercomponents. Further, providing a consistent distance between the FETs1540 and the ribs 1546 facilitates estimating the amount and thicknessof the thermal interfacial material 1544 to be disposed therebetween.

In examples, the motor 1502 may be a three-phase motor that has threewindings or phases positioned 120□ electrically apart. The stator of themotor 1502 may include 12 slots windings, and may thus have 12 wirescoming out thereof. These 12 wires can be arranged into severalconfigurations such as delta, star, parallel, or series configurations.The configuration may affect the performance and torque output of themotor 1502.

Although 12 wires come out of the stator, after configuring the wiresinto a star, parallel, or series configuration, the number of wires isreduced to 3 or 6 wires to be received at the controller 1508. Tofacilitate the interface between the 12 wires coming out of the statorand the controller 1508, a phase board 1552 may be disposedtherebetween. The phase board 1552 operates as an intermediate ortransition board between the stator of the motor 1502 and the controller1508.

FIG. 15E illustrates 12 wires emanating from a stator 1554 of the motor1502, and FIG. 15F illustrates the phase board 1552 configured tointerface with the stator 1554, in accordance with an exampleimplementation. The stator 1554 presents 12 individual winding wiressuch as wires 1555A and 1555B. The phase board 1552 is configured toreceive the 12 wires from the stator 1554 and includes conductive linestherein that make the final connection into star, delta, parallel, orseries desired configuration. The phase board 1552 then presents 3 or 6pins such as pins 1556A and 1556B to the controller 1508, i.e., to thepower stage PCB 1510. With this configuration, the phase board 1552transitions the wires coming out of the stator 1554 into robust pins tobe received at connectors of the power stage PCB 1510. Thisconfiguration reduces wiring complexity and increases reliability andenhances the ability to repair the assembly 1500.

In examples, the phase board 1552 may be coupled (e.g., glued via anytype of adhesive) to the stator 1554. To change the wiring configuration(e.g., from star to delta), the phase board 1552 may be removed and adifferent phase board that realizes the desired wiring configuration maybe coupled to the stator 1554 without changes to the stator 1554. Inthis manner, minimal changes are performed on the stator 1554, and therisk of damaging the stator 1554 is reduced.

Similarly, no changes or minimal changes are performed to the controller1508. The replacement phase board would provide the same number of pinsto the controller 1508. In this manner, the risk of damaging thecontroller 1508, which could be expensive, is reduced.

FIG. 15G illustrates an exploded view of the assembly 1500, inaccordance with an example implementation. The exploded view in FIG. 15Gfurther illustrates the relationship and order of assembly of variouscomponents of the assembly 1500. In an example, as shown in FIG. 15G, anelectric insulation sheet 1558 could be disposed between the phase board1552 and the housing 1504 to ensure electric insulation therebetween.

As such, the integration the motor 1502 and the controller 1508 andsharing of components allows for reducing the size and complexity of theassembly 1500. Further, the likelihood of wire damage is reduced, andreliability of the assembly 1500 is increased. The increase inreliability is magnified for the robot as a whole given that the robotmay include many assemblies similar to the assembly 1500.

III. Conclusion

The arrangements described herein are for purposes of example only. Assuch, those skilled in the art will appreciate that other arrangementsand other elements (e.g., machines, interfaces, operations, orders, andgroupings of operations, etc.) can be used instead, and some elementsmay be omitted altogether according to the desired results. Further,many of the elements that are described are functional entities that maybe implemented as discrete or distributed components or in conjunctionwith other components, in any suitable combination and location.

While various aspects and implementations have been disclosed herein,other aspects and implementations will be apparent to those skilled inthe art. The various aspects and implementations disclosed herein arefor purposes of illustration and are not intended to be limiting, withthe true scope being indicated by the following claims, along with thefull scope of equivalents to which such claims are entitled. Also, theterminology used herein is for the purpose of describing particularimplementations only, and is not intended to be limiting.

What is claimed is:
 1. A robot comprising: a motor disposed at a joint of a leg of the robot, the motor configured to control motion of the leg of the robot; a transmission comprising an input member coupled to and configured to rotate with the motor, an output member, and a fixed intermediate member that engages the output member, the input member configured to engage the fixed intermediate member and rotate within an open annular space defined by the fixed intermediate member, and when the input member rotates, the output member rotates at a different speed; a pad frictionally coupled to a side surface of the output member of the transmission and coupled to the leg of the robot; a spring configured to apply an axial preload on the pad, the axial preload defining a torque limit that indicates a torque load on the leg of the robot that causes the output member of the transmission to slip relative to the pad; and an output flexure member disposed between, and interfacing with, the pad and the spring, wherein the output flexure member is torsionally stiff and axially flexible, and wherein the output flexure member is coupled to the leg of the robot.
 2. The robot of claim 1, wherein the joint corresponds to a hip joint of the leg of the robot.
 3. The robot of claim 2, further comprising a housing at the hip joint of the leg of the robot, wherein the motor is disposed within the housing.
 4. The robot of claim 1, wherein the robot comprises a quadruped robot.
 5. The robot of claim 1, wherein the robot comprises a biped robot.
 6. The robot of claim 1, further comprising a second pad frictionally coupled to a proximate side surface of the output member, and wherein the pad is frictionally coupled to a distal side surface of the output member of the transmission.
 7. The robot of claim 6, wherein the second pad is coupled to a presser plate, the presser plate coupled to the leg of the robot.
 8. The robot of claim 1, further comprising a constraint ring coupled to the leg of the robot, the constraint ring defining the open annular space where the output member of the transmission is mounted.
 9. The robot claim 8, further comprising a constraint bushing mounted between the constraint ring and the output member of the transmission, the constraint bushing comprising an exterior peripheral surface interfacing with an interior peripheral surface of the constraint ring and an interior peripheral surface interfacing with an exterior peripheral surface of the output member of the transmission.
 10. The robot of claim 1, further comprising an O-ring mounted within a second annular space defined by the pad.
 11. The robot of claim 1, wherein: the input member is elliptically shaped and configured to cause the intermediate member to deform as the input member rotates; the fixed intermediate member comprises external teeth disposed on an external peripheral surface of the intermediate member; and the output member comprises internal teeth disposed on an interior peripheral surface of the output member, the internal teeth configured to engage the external teeth of the intermediate member.
 12. An assembly comprising: a motor disposed at a hip joint of a leg of a robot, the motor configured to control motion of the leg of the robot; a harmonic drive comprising a wave generator coupled to and configured to rotate with the motor, a flexspline, and a circular spline, and when the wave generator rotates, the flexspline is fixed while the circular spline rotates with the wave generator at a different speed; a first pad frictionally coupled to both a distal side surface of the circular spline and the leg of the robot; a second pad frictionally coupled to a proximal side surface of the circular spline; a compliant member configured to apply an axial preload on the first and second pads, the axial preload defining a torque limit, and when a torque load on the leg of the robot satisfies the torque limit, the circular spline slips relative to at least one of the first or second pads; and an output flexure member disposed between and interfacing with the first pad and the compliant member, the output flexure member coupled to the leg of the robot.
 13. The assembly of claim 12, wherein the robot comprises a quadruped robot having four legs, and wherein the leg comprises one leg of the four legs of the quadruped robot.
 14. The assembly of claim 12, wherein the robot comprises a biped robot having two legs, and wherein the leg comprises one leg of the two legs of the biped robot.
 15. The assembly of claim 12, wherein the second pad is coupled to a presser plate, the presser plate coupled to the leg of the robot.
 16. The assembly of claim 15, further comprising a constraint ring coupled to the leg of the robot, the constraint ring defining an open annular space, the circular spline and the first and second pads frictionally coupled to the circular spline mounted within the open annular space, the presser plate coupled to the leg of the robot by a radial array of bolts that couple the presser plate to the constraint ring.
 17. The assembly of claim 16, further comprising a cross-roller bearing mounted between an exterior peripheral surface of the constraint ring and an interior surface of a housing of the motor.
 18. The assembly claim 12, further comprising a constraint bushing mounted between the constraint ring and the circular spline, the constraint bushing comprising an exterior peripheral surface interfacing with an interior peripheral surface of the constraint ring and an interior peripheral surface interfacing with an exterior peripheral surface of the circular spline.
 19. The assembly of claim 12, wherein the first pad defines a first open annular space and the second pad defines a second open annular space, the assembly further comprising: a first O-ring mounted within the first open annular space defined by the first pad; and a second O-ring mounted within the second open annular space defined by the second pad.
 20. The assembly of claim 12, wherein the flexspline comprises a thin-walled cylinder with external teeth formed circumferentially on a portion of an outer surface of the thin-walled cylinder, and the assembly further comprises a torque sensor mounted on a housing of the motor and coupled to a portion of the thin-walled cylinder.
 21. The assembly of claim 12, wherein the compliant member comprises a Belleville spring.
 22. An assembly comprising: a motor disposed at a hip joint of a leg of a robot, the motor configured to control motion of the leg of the robot; a harmonic drive comprising: a wave generator coupled to and configured to rotate with the motor; a flexspline; and a circular spline, and when the wave generator rotates, the flexspline is fixed while the circular spline rotates with the wave generator at a different speed, wherein the flexspline comprises a thin-walled cylinder with external teeth formed circumferentially on a portion of an outer surface of the thin-walled cylinder; a torque sensor mounted on a housing of the motor and coupled to a portion of the thin-walled cylinder; a first pad frictionally coupled to both a distal side surface of the circular spline and the leg of the robot; a second pad frictionally coupled to a proximal side surface of the circular spline; and a compliant member configured to apply an axial preload on the first and second pads, the axial preload defining a torque limit, and when a torque load on the leg of the robot satisfies the torque limit, the circular spline slips relative to at least one of the first or second pads. 